Melatonin maintains postharvest quality by modulating the metabolisms of cell wall and sugar in flowering Chinese cabbage

Melatonin is known to delay postharvest nutrient loss. However, its specific roles in regulating cell wall and sugar metabolism to maintain postharvest quality in flowering Chinese cabbage remain unclear. In this study, postharvest flowering Chinese cabbage was treated with melatonin (100 µmol L^{- 1}) to investigate the cell wall and sugar metabolisms. Our research found that melatonin supplementation increased levels of important nutrients like ascorbic acid, sugars, soluble protein, carotenoid, and glucosinolates. It also enhanced various cell wall components (cellulose, hemicellulose, lignin, and protopectin) while reducing water-soluble pectin accumulation. Melatonin helped stabilize cell wall by reducing the expression of genes related to cell wall degradation (BrBGAL4, BrPG, BrCEL3, and BrPME3), inhibiting activities of cell wall-degrading enzymes like pectin methylesterase and cellulase, and improving expressions of cellulose biosynthesis-related genes (BrCesA1, BrCesA3.1, and BrCesA3.2). Additionally, it boosted sugar accumulation by increasing activities of sucrose synthetase and sucrose phosphate synthetase, upregulating expressions of BrSUS1, BrSUS5, BrSPS1F, BrSPS3F, BrSPS4F, and suppressing activities of neutral invertase and acidic invertase and expressions of genes involved in sugar metabolism (BrSUS3, BrINV, BrSWEET2, BrSWEET4, and BrSWEET17). This study highlights melatonin's vital roles in maintaining postharvest quality and offers practical insights for improving market performance of flowering Chinese cabbage.